docs(github): move markdown files into .github folder

.github/ISSUE_TEMPLATE.md

+Thank you! For helping us make Grafana even better.
+
+To help us respond to your issues faster, please make sure to add as much information as possible.
+
+If this issue is about a plugin, please open the issue in that repository.
+
+Tag your issues title with [Feature Request] / [Bug] / [Question] or no tag if your unsure.
+
+Ex
+* What grafana version are you using?
+* What datasource are you using?
+* What OS are you running grafana on?